Swedish patent application No. 78.03046-7 (U.S. Ser. No. 779 152 filed Mar. 18, 1977, which is the parent of U.S. patent application Ser. No. 41,551, filed May 23, 1979, now U.S. Pat. No. 4,317,367) and the two copending PCT Applications PCT/SE78/00012 (U.S. patent application Ser. No. 131,079, filed July 3, 1978, now U.S. Pat. No. 4,269,633) and PCT/SE78/00013 (U.S. patent application Ser. No. 131,078, filed June 1, 1979, now U.S. Pat. No. 4,253,334) describe different embodiments of an apparatus similar to that according to the invention and how the apparatus according to the invention may be used. The concept forming the basis of the present invention is, in this instance, to realize such an apparatus, but of simpler type and adapted to a simpler manner of manufature.
In U.S. patent applications Ser. No. 787,422, filed Apr. 14, 1977, now U.S. Pat. No. 4,200,970 and Ser. No. 879,193, filed Feb. 21, 1978) there are described different trimming processes for apparatuses similar to that according to the invention. Such trimming processes could well be used for trimming the apparatus according to the invention. Preferably however, use is made instead of an assortment of the type described in co-filed application PCT/SE78/00012 (U.S. patent application Ser. No. 131,079, filed July 3, 1978, now U.S. Pat. No. 4,296,633).